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Grab a pint of guinness in the garrick. Take the missus to margot for cocktails.
High end grub head to the muddlers club (might struggle to get a table at this short notice.)
Mid level food in mumbai 27, ginger bistro, edo, zen, mr deanes/meat locker, howard st or home. All decent.
Sat night around the cathedral quarter will be busy. Some decent-ish pubs around there.
Titanic museum and the gin distillery tour are closer to home than heading up to the giants causeway but obviously not just as scenic.